diff --git a/internal/hooks/postcommit.go b/internal/hooks/postcommit.go
index 0cd65b1..ee395b7 100644
--- a/internal/hooks/postcommit.go
+++ b/internal/hooks/postcommit.go
@@ -6,6 +6,7 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/partio-io/cli/internal/agent/claude"
@@ -13,6 +14,7 @@ import (
 	"github.com/partio-io/cli/internal/checkpoint"
 	"github.com/partio-io/cli/internal/config"
 	"github.com/partio-io/cli/internal/git"
+	"github.com/partio-io/cli/internal/session"
 )
 
 // PostCommit runs post-commit hook logic.
@@ -141,6 +143,28 @@ func runPostCommit(repoRoot string, cfg config.Config) error {
 		return fmt.Errorf("writing checkpoint: %w", err)
 	}
 
+	// Update session activity: count files changed in this commit
+	numstat, _ := git.DiffNumstat(commitHash)
+	filesChanged := countNumstatFiles(numstat)
+	mgr := session.NewManager(filepath.Join(repoRoot, config.PartioDir))
+	if err := mgr.RecordActivity(filesChanged); err != nil {
+		slog.Warn("could not update session activity", "error", err)
+	}
+
 	slog.Debug("checkpoint created", "id", cpID, "agent_pct", attr.AgentPercent)
 	return nil
 }
+
+// countNumstatFiles counts the number of files from git diff --numstat output.
+func countNumstatFiles(numstat string) int {
+	if numstat == "" {
+		return 0
+	}
+	count := 0
+	for _, line := range strings.Split(numstat, "\n") {
+		if strings.TrimSpace(line) != "" {
+			count++
+		}
+	}
+	return count
+}
diff --git a/internal/session/manager.go b/internal/session/manager.go
index bf9a7c0..6a92d89 100644
--- a/internal/session/manager.go
+++ b/internal/session/manager.go
@@ -5,6 +5,9 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
+	"strings"
+	"time"
 )
 
 // Manager handles session lifecycle transitions.
@@ -24,9 +27,72 @@ func (m *Manager) save(s *Session) error {
 	if err != nil {
 		return fmt.Errorf("marshaling session: %w", err)
 	}
+	if err := os.WriteFile(m.idPath(s.ID), data, 0o644); err != nil {
+		return fmt.Errorf("saving session by id: %w", err)
+	}
 	return os.WriteFile(m.currentPath(), data, 0o644)
 }
 
 func (m *Manager) currentPath() string {
 	return filepath.Join(m.stateDir, "current.json")
 }
+
+func (m *Manager) idPath(id string) string {
+	return filepath.Join(m.stateDir, id+".json")
+}
+
+// List returns all sessions sorted by most recent activity, newest first.
+func (m *Manager) List() ([]*Session, error) {
+	entries, err := os.ReadDir(m.stateDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("reading sessions dir: %w", err)
+	}
+
+	var sessions []*Session
+	for _, e := range entries {
+		if e.IsDir() || e.Name() == "current.json" || !strings.HasSuffix(e.Name(), ".json") {
+			continue
+		}
+		data, err := os.ReadFile(filepath.Join(m.stateDir, e.Name()))
+		if err != nil {
+			continue
+		}
+		var s Session
+		if err := json.Unmarshal(data, &s); err != nil {
+			continue
+		}
+		sessions = append(sessions, &s)
+	}
+
+	sort.Slice(sessions, func(i, j int) bool {
+		ti := latestTime(sessions[i])
+		tj := latestTime(sessions[j])
+		return ti.After(tj)
+	})
+
+	return sessions, nil
+}
+
+// RecordActivity updates a session's last activity time and cumulative files modified count.
+func (m *Manager) RecordActivity(filesChanged int) error {
+	s, err := m.Current()
+	if err != nil || s == nil {
+		return err
+	}
+	s.UpdatedAt = time.Now()
+	s.FilesModified += filesChanged
+	return m.save(s)
+}
+
+func latestTime(s *Session) time.Time {
+	if !s.EndedAt.IsZero() {
+		return s.EndedAt
+	}
+	if !s.UpdatedAt.IsZero() {
+		return s.UpdatedAt
+	}
+	return s.StartedAt
+}
diff --git a/internal/session/session.go b/internal/session/session.go
index 67c234c..615e2a8 100644
--- a/internal/session/session.go
+++ b/internal/session/session.go
@@ -8,13 +8,15 @@ import (
 
 // Session represents an AI agent coding session.
 type Session struct {
-	ID        string    `json:"id"`
-	Agent     string    `json:"agent"`
-	State     State     `json:"state"`
-	StartedAt time.Time `json:"started_at"`
-	EndedAt   time.Time `json:"ended_at,omitempty"`
-	Branch    string    `json:"branch"`
-	SourceDir string    `json:"source_dir"`
+	ID            string    `json:"id"`
+	Agent         string    `json:"agent"`
+	State         State     `json:"state"`
+	StartedAt     time.Time `json:"started_at"`
+	EndedAt       time.Time `json:"ended_at,omitempty"`
+	UpdatedAt     time.Time `json:"updated_at,omitempty"`
+	Branch        string    `json:"branch"`
+	SourceDir     string    `json:"source_dir"`
+	FilesModified int       `json:"files_modified,omitempty"`
 }
 
 // New creates a new session with a generated UUID.